Professional Mobile Radio (PMR), also known as land mobile radio (LMR) in North America and private mobile radio (PMR) in the UK, was developed for business users who need to communicate over relatively short distances with a central base station/dispatcher. PMR systems may be used in military, oil and gas, public security, rail transport, emergency, and various other applications.
PMR systems have generally been based on analog technology. To increase spectrum efficiency as well as improve communication quality, various jurisdictions plan to migrate from analog to digital PMR/LMR. DMR (Digital Mobile Radio) is a digital radio standard for Professional Mobile Radio (PMR) systems. Requirements of the DMR standard include a 12.5 kHz channel that supports two independent transmissions via radio frequency signals. Thus, under the DMR standard, utilizing Time Division Multiple Access (TDMA), the 12.5 kHz channel is divided into two alternating time slots which each act as a separate communication channel with an equivalent bandwidth of 6.25 kHz. The frequency synthesizers employed in digital radio systems often employ a phase locked loop to generate the radio frequency signals.